In anesthetized and/oor decerebrate cats we propose to determine if motor neurons that have an inspiratory pattern regulate airway tone and to establish that respiratory rhythm is generated in the medulla by two paired respiratory pattern generators having different power spectral densities. We hope to demonstrate that these pattern generators are separate from the identified population of respiratory units in the ventrolateral portion of the nucleus tractus solitarius and in the nucleus ambiguus or nucleus retroamibualis. To localize units which have the characteristics of a pattern generator we shall record either intracellular potentials or extracellular spike activity of respiratory units driven by iontophoretic application of a nonspecific transmitter. We shall characterize these units by their response to ventilatory reflexes and the spectral density of their activity. We also propose to measure changes in airway tone and smooth muscle tone in a tracheal segment and to correlate spontaneous changes as well as reflex-induced changes with phrenic activity. We will also record intracellular potentials from tracheal parasympathetic ganglia and tracheal smooth muscle to determine if the synaptic input has a respiratory rhythm.